Infrared and submillimetre observations of the ρ Ophiuchi dark cloud.

A survey of part of the ρ Ophiuchi dark cloud region at wavelengths from 2 to 1100 μm is presented. The IRAS source 16235-2416 is identified with a previously discovered 80-μm source. A new method of background subtraction for IRAS raw data is outlined. A new submillimetre source, SM1 is reported, which is a cool condensation of dust. The continuum fluxes of SM1 are fitted with a greybody spectrum with dust grain temperature 15±5K. The mass and density of SM1 are such that it is a candidate protostellar object. The grain emissivity coefficient β is found to be 2.2±0.3 at submillimetre wavelengths, a value usually taken to be indicative of the presence of grain mantles. A new, intermediate-resolution spectrum around 2-4 μm shows the distinctive absorption feature at 3.07 μm attributed to water-ice, confirming the presence of solid H₂O on dust grains. The visual extinction (A_V = 12) is lower than that usually associated with grain mantling in the ρ Oph dark cloud complex.